Skeletons' teeth acted like time capsules from London's Great Plague

Between the years 1665 and 1666, London's people suffered the last major epidemic of the bubonic plague that would strike England, also referred to as the Great Plague. Despite killing approximately 100,000 people – nearly a quarter of the city's population – archeologists have struggled to find hard-and-fast traces of it in skeletal remains due to the fast-acting nature of the disease, which leaves afflicted bones with no DNA evidence. Now, the teeth samples of five skeletons from a mass grave excavated from London's Bedlam burial ground, also referred to as the New Churchyard, have been found to contain the DNA of plague-causing bacteria Yersinia pestis for the first time.

After the discovery of the mass grave last summer, osteologists from the Museum of London Archaeology (MOLA) retrieved samples from the teeth of 20 individuals from the site. The team sent the samples to the Max Planck Institute in Germany, where testing eventually revealed the presence of DNA from Y. pestis in five of them.

Scientists believe that the enamel shells of the teeth preserved the DNA from the pathogen, "essentially acting as little time capsules" according to MOLA, and ultimately allowing us to look back in time to discover clear evidence of the plague in the London community.

Although only five samples tested positive for the bacteria, the MOLA team stresses that the survival rate of ancient DNA over hundred-year time periods is low, meaning the possibility that more from the site died at the hands of the disease is not out of the question.

The revelation of Y. pestis as the bacteria species behind England's last bubonic plague isn't a surprise. In fact, it has been responsible for three other major epidemics throughout history: the Plague of Justinian, the Black Death and the Third Pandemic. It is typically transmitted through flea bites, contact with contaminated fluid or tissue, or infectious cough droplets.

Over the coming months, further analysis will attempt to reveal more detail on the individuals from the gravesite who tested positive for Y. pestis. Researchers hope to use isotopic analysis to determine where they grew up and migrated within their lifetime, as well as examine materials within the plaque of their teeth to determine their diets and the diseases and pollutants that they were exposed to.

The five skeletons that yielded the DNA from a plague-causing bacteria in their teeth(Credit: Crossrail Limited)

Although only five out of 20 skeletons were found to have the plague-causing bacteria, more may have died from the disease as DNA is fragile and could have degraded over the years(Credit: Museum of London Archaeology)